1. Field of the Invention
This invention relates to an apparatus and method for implanting a conduit to allow communication of fluids from one portion of a patient's body to another; and, more particularly, to a blood flow conduit to allow communication from a heart chamber to a vessel or vice versa, and/or vessel to vessel. Even more particularly, the invention relates to a left ventricular conduit and related conduit configurations for controlling the flow of blood through the conduit to achieve bypass of an occluded coronary artery.
2. Description of Related Art
Coronary artery disease is a major problem in the U.S. and throughout the world. In fact, about 1.1 million “open heart” procedures are performed each year, and current estimates are that approximately 4.8 million people suffer from some degree of congestive heart failure.
When coronary arteries or other blood vessels become clogged with plaque, the results are at the very least impairment of the efficiency of the heart's pumping action. On the more severe side of the scale are heart attack and death. In some cases, clogged arteries can be unblocked through minimally invasive techniques such as balloon angioplasty. In more difficult cases, a surgical bypass of the blocked vessel is necessary.
In a bypass operation, one or more arterial or venous segments are harvested from the body and then surgically inserted between the aorta and the coronary artery. The inserted vessel segments, or transplants, act as a bypass of the blocked portion of the coronary artery and thus provide for a free or unobstructed flow of blood to the heart. More than 500,000 bypass procedures are performed in the U.S. every year.
Coronary artery bypass grafting (CABG) has been used for more than 30 years. Initially, the saphenous vein (SV) served as the principal conduit for coronary bypass, but studies over the last dozen years have shown a 35–40% increase in 10-year patency rate for the internal thoracic artery (ITA) compared with the SV. The SV, in fact, has only been shown to have a 10-year patency rate of 50%. Since the mid 1980's, not only the ITA, but also the alternative arterial conduits have been increasingly used. These conduits include the grastroepiploic artery (GEA), inferior epigastric artery (IEA), and radial artery (RA), which have been used primarily as supplements to both the right and left ITA.
Although the use of arterial conduits results in demonstrably better long-term patency, use of arteries in place of the SV often requires complex technical challenges, such as free grafts, sequential anastomosis, and conduit-to-conduit anastomosis. Some of the reasons for the difficulty in using arterial conduits reside in the fact that they are much more fragile than the SV and therefore easier to damage, and due to their smaller size, easier to occlude completely or partially through technical error during grafting.
Such coronary artery bypass surgery, however, is a very intrusive procedure that is expensive, time-consuming and traumatic to the patient. The operation requires an incision through the patient's sternum (sternotomy), and the patient be placed on a bypass pump so that the heart can be operated on while not beating. A vein graft is harvested from the patient's leg, another highly invasive procedure, and a delicate surgical procedure is required to piece the bypass graft to the coronary artery (anastomosis). Hospital stays subsequent to the surgery and convalescence periods are prolonged.
As mentioned above, another conventional treatment is percutaneous transluminal coronary angioplasty (PTCA) or other types of angioplasty. However, such vascular treatments are not always indicated due to the type or location of the blockage, or due to the risk of the emboli formation.
One bypass technique employed in the prior art is taught by Wilk (U.S. Pat. Nos. 5,287,861, 5,409,019, 5,662,124, and 5,429,144, the entirety of each of which is hereby incorporated herein by this reference). These Wilk references teach the use of a stent which is introduced through the myocardial wall from an adjacent coronary artery to provide a bypass conduit between the left ventricle and the adjacent coronary artery. In one embodiment, this technique teaches the delivery of a transmyocardial bypass shunt in a collapsed, reduced-profile configuration, which requires radial expansion subsequent to delivery in a bore preformed in the myocardial wall. The bore is formed, for example, by a drill, needle, Seldinger wire, dilating wires or catheters, or other devices prior to stent placement and expansion.
In another embodiment, Wilk discloses the disposition of a stent in the myocardium so that the stent extends only in the myocardium. The stent may extend only partially through the myocardium, from the left ventricle of the heart or from a coronary artery, upstream of a vascular obstruction. Alternatively, the stent may extend completely through the myocardium to establish a blood flow path or conduit from the left ventricle to a coronary artery, downstream of a vascular obstruction.
Where stents are used in the Wilk cardiac revascularization techniques to guide blood from the left ventricle, the stents may be designed to lock upon opening from collapsed insertion configurations. Such stents enable the infusion of blood into the myocardium during systole. The stents may be provided with one-way valves to regulate or control the backflow of blood during diastole.
Thus, there is a continuing need for improved bypass methods and apparatus that allow for the realization of increased long-term patency rates, and that are less physically traumatic to the patient.